Project Abstract Current rates of prescription opioid misuse are rising to epidemic levels among adults. These rates may be even higher among adolescents and young adults (AYA's), who have elevated levels of substance exploration and misuse during this precise developmental period. AYA who are exposed to opioids via legitimate prescriptions by age 18 are at increased risk for misuse after high school. However, there is a substantial gap in our knowledge of what factors might contribute to the development of misuse and related poor outcomes in these high-risk youth. Identifying factors that convey risk for increasing opioid use and problematic use would inform AYA models of opioid abuse and inform the development of preventive interventions to modify risk in the medical setting. Medical settings, where AYA's are exposed to opioids via legitimate prescription is a unique point of entry into opioid use, and a key setting in which to examine AYA outcomes. The proposed study will utilize a developmental model of the impact of opioid exposure by legitimate prescription during late adolescence, with consideration for pain and psychological characteristics of the individual within the psychosocial (family, peer, and educational and work context). Predictors and mechanisms of increasing opioid use and problematic use will be examined over a two year time period. The central hypothesis is that AYA pain characteristics will influence opioid use and problems over time, and that opioid availability will mediate this association. Longitudinal models of opioid use and opioid problems will be tested in a sample of n=100 18-25 year olds receiving opioid prescriptions for non-cancer pain in outpatient medical settings. Participants will report on pain characteristics, opioid and other substance use and problems, peer factors, as well as pain catastrophizing and other pain related psychological factors. Objective data on dispensed opioid medications will be obtained from prescription drug monitoring databases. Daily associations between pain, pain catastrophizing, and opioid use will also be examined via electronic diary methodology. Determining mechanisms and moderators of risk during this developmental transition will provide critical information for the design of interventions aimed at reducing opioid use disorders in at-risk AYA.